1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to an in-line type electron gun in a color cathode ray tube, which can improve a focusing characteristic.
2. Background of the Related Art
In general, electrodes in the in-line type electron guns are positioned at intervals to each other vertical to electron beam paths for controlling the electron beams to reach to a screen in a required form, which will be described in detail, with reference to FIG. 1 illustrating a section of a related art cathode ray tube.
Referring to FIG. 1, the in-line type electron gun is provided with three cathodes 10 independent from one another, a first electrode 11 which is a common electrode for the three cathodes, and a second electrode 12, a third electrode 13, a fourth electrode 14, a fifth electrode 15, and a sixth electrode 16, each spaced a distance away from each other. Moreover, there is a shield cup 17 above the sixth electrode 16, and there is a B.S.C (Bulb Space Connector) 18 attached to the shield cup for electrical connection of the electron gun to the tube and fastening the electron gun to a neck portion 3 of the tube. Accordingly, the electron beams 4 are emitted from heaters (not shown) each built-in the respective cathodes 10, controlled by the first electrode 11 which is a control electrode, accelerated by the second electrode 12 which is an accelerating electrode, pre-focused/accelerated by a pre-focus lens formed by the second electrode 12, the third electrode 13, the fourth electrode 14, and the fifth electrode 15, and mainly focused/accelerated by the fifth electrode 15 which is called as a focus electrode and the sixth electrode 16 which is called as an anode, both form a main lens. Then, the electron beams 4 pass through a shadow mask 1 which selects colors, and collide on a fluorescent surface 2, to make the fluorescent surface luminescent. Eventually, the electron beams 4 from the electron gun can form a picture by means of a deflection yoke, which deflects the electron beams to the entire screen.
FIG. 2 illustrates a perspective view of one example of a related art main lens forming electrode, and FIG. 3 illustrates a front view of an electrostatic field controlling electrode in the related art main lens forming electrode.
Referring to FIG. 2, the main lens forming electrode is provided with the focus electrode 15 and the anode 16, each with a rim part 15a and 16a in a form of a running track common for the three electron beams at positions to face each other, and the electrostatic field controlling electrode 25 and 26 as shown in FIG. 3 at a position inside of the focus electrode 15 or the anode 16. The electrostatic field controlling electrode 25 or 26 is a plate having three circular pass through holes 25a and 26a, for enlarging a main lens diameter.
The foregoing main lens forming electrode has the following problems.
Before explaining the problems, factors that give influences to a spot diameter on a picture will be explained. In general, as electron gun design criteria that influences the spot diameter on the picture, there are lens magnitudes, space charge repelling powers, and a main lens spherical aberration. The influence of the lens magnitude to the spot diameter Dx that can be utilized as the design criteria for the electron gun is little and has a slight effect too, because basic voltage conditions, focal distances, a length of the electron gun, and the like are fixed. As the space charge repelling power enlarges the spot diameter Dst owing to repellence and collision between the electrons, and it is favorable to design an angle of the electron beam divergence (called as a divergence angel) great for reducing the enlargement of the spot diameter Dst caused by the space charge repelling power. Opposite to this, the spherical aberration of the main lens, a characteristic representing an enlargement of the spot diameter Dic caused by a difference of focal distances of electrons passed through a radical axis and passed through a protaxis, forms the smaller spot diameter on the screen as the divergence angle is the smaller. In general, the spot diameter Dt on the screen can be expressed by using the following three parameters.       D    t    =                              (                                    D              x                        +                          D              st                                )                2            +              D        ic        2            
Particularly, as the best method for reducing the spherical aberration together with a reduction of the space charge repelling force, the main lens with a larger diameter is provided. However, the greater rim parts 15a and 16a and the greater depth of the electrostatic field controlling electrode 25 and 26 from the rim parts 15a and 16a to the electrostatic field controlling electrode 25 and 26 for providing a greater diametered main lens causes the following deterioration of the electron beam spot. As shown in FIG. 3, the electrostatic field controlling electrode 25 or 26 has pass through holes 25a and 26b for passing the three electron beams of R, G, B beams, wherein the center beam, the G beam, passes thorough the center beam pass through hole 25b, and the outer beams, R and B beams, pass through the outer beam pass through holes 25a, each a distance away from the center beam pass through hole 25b in opposite directions. That is, FIG. 4 illustrates forms of spots according to one exemplary related art main lens forming electrode.
Referring to FIG. 4, each of the spots formed by the outer electron beams has a form similar to an isosceles triangle, with an apex xe2x80x98Axe2x80x99 thereof at which two equal sides xe2x80x98Bxe2x80x99 thereof meet together positioned at an outer side (an opposite side of the center beam side) and halos along the two equal sides thereof, that deteriorate the outer beam spots, because the rim part 15a of the focus electrode 15 weakens the focusing power at upper and lower portions of an inside portion of the outer beam (a center beam side) and enhances the focusing power at upper and lower portions of an outside (opposite sides of the center beam) of the outer beam. This may be explained extensively as follows. Alike a rubber ball with full of air, that bulges at the other side if one side is pressed, if the focusing power at the outside of the electron beam is enhanced, the focusing power of the inside of the electron beam is weakened, to show spot forms similar to the isosceles triangles on the screen. Moreover, there are fine halos formed along the two equal sides xe2x80x98Bxe2x80x99. Though the anode 16 can correct the spots of the outer beams slightly as the anode 16 acts opposite to the action of the focus electrode 15, since the main lens enhances the focusing power by the focus electrode more than acceleration by the anode, a spot form by the focusing power only is exhibited at the end.
FIG. 5 illustrates a perspective view of another example of a related art main lens forming electrode, FIG. 6A illustrates a front view of an electrostatic field controlling electrode in a focus electrode of a related art main lens forming electrode, and FIG. 6B illustrates a front view of an electrostatic field controlling electrode in an anode of a related art main lens forming electrode.
Referring to FIG. 5, another example of the related art main lens forming electrode 15 is provided with a focus electrode 15, an anode 16, rim parts 15a and 16a of track forms at opposite sides of the focus electrode 15 and the anode 16 respectively for three electron beams in common, and electrostatic field controlling electrodes 35 and 36 insides of the focus electrode 15 and the anode 16 at distances away from the rim parts as shown in FIGS. 6A and 6B, respectively. As shown in FIG. 6A, the electrostatic field controlling electrode 35 in the focus electrode 15 has a form of plate with three vertically elongated pass through holes 35a and 35b, for enlarging a diameter of the main lens. As shown in FIG. 6B, the electrostatic field controlling electrode 36 in the anode 16 has a form of plate with a circular pass through hole 36a, for accelerating the electron beams. The foregoing another example of the related art main lens forming electrode 15 has the following problems. Though the focusing of the focus electrode 15 in another example of the related art main lens forming electrode 15 is similar to the example, because the diverging action is very weak relative to the example owing to the weakened acceleration of the anode 16 coming from the position of the electrostatic field controlling electrode distanced far from the rim part 16a, the spot forms of the outer electron beams on the screen are exhibited as shown in FIG. 7 that is opposite to the FIG. 4.
In conclusion, the example and another example of the related art main lens forming electrodes have the following problems.
The difference between the center beam and the other beam caused by the main lens acting on the outer beams forms vertical fine halo at a central portion of the screen, and distorted spot forms at a peripheral region of the screen failing to focus a clear spot, thereby failing to make focusing meeting the requirements for high resolution, large sized screen, planarization of the screen, and provision of a large angled view.
In order to form the outer beam spots circular, the related art electron gun requires much care in assembly that results in drop of productivity of the electron gun, because formation of the one sided halo is sensitive to an accuracy of assembly of the electron gun with respect to alignment of the holes and a flatness of the electrodes.
Accordingly, the present invention is directed to an in-line type electron gun in a color cathode ray tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an in-line type electron gun in a color cathode ray tube, in which a structure of the main lens forming electrode is improved for an excellent focusing and improved assembly work.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the in-line type electron gun in a color cathode ray tube includes a pre-focusing lens part having at least two electrodes for focusing electron beams, a main lens part having two, or more than two electrodes for focusing the electron beams onto a screen, and at least one electrostatic field controlling electrode in the electrodes of the main lens part having a center electron beam pass through hole and two outer electron beam pass through holes, wherein each of the outer electron beam pass through holes has a form a circular hole and a rectangular hole are combined therein, the rectangular hole having a height xe2x80x98V2xe2x80x99 greater than a vertical diameter xe2x80x98V1xe2x80x99 of the center beam pass through hole of the electrostatic field controlling electrode.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.